DESCRIPTION: Work-related low back musculoskeletal disorders are common and affect a large portion of the workforce. Occupational risk factors for LBP include sustained static muscle load, and inappropriate curvature/position of the spine and pelvis. Sitting may cause backward rotation of the pelvis, reduction in lumbar lordosis, changes in muscle activities and disc pressure, excessive pressure over the ischium and coccyx, and certainly the associated LBP. A new seat design, of which the back part of seat (BPS) can be dynamically tilted downward and upward with respect to the front part of the seat (FPS) providing adjustment of thigh and ischial support and the back support is adjustable in height and volume, will be investigated. It was found in the pilot study that sitting with lowered BPS and adjustment of low back support resulted in more evenly distributed contact pressure, reduced peak pressure under the ischia, increased total and segmental lumbar lordosis, forwardly rotated the pelvis, and increased lumbar intervertebral heights. We believe that the functional relations of the seat and backrest need to be further investigated in order to not only prevent flattening of the lumbar spine but also reduce the ischial load in long term sitting, which are related to LBP. We propose to study the biomechanical and neuromuscular effects of the new sitting concept, and evaluate quantitatively the benefits in the LBP patients for using appropriate lumbar support that increases lordosis and decreases the sitting pressure and load carried by the ischial tuberosities. Hypothesis 1: When the BPS is tilted downward, load on the ischial tubercles and lumbar spine will be reduced and shifted to the thighs and the thoracic spine, respectively. Low back muscle activities will also be reduced. Specific aim 1: Contact pressure distributions between the buttock-thighs and seat, and between the back and backrest, load carried at the seat and back will be evaluated with and without ischial support, combined with flat or adjusted back support. The muscular activities involved in stabilizing the trunk under these conditions will be investigated. Hypothesis 2: Increase in lumbar lordosis, forward rotation of the pelvis, and larger intervertebral heights will be observed when the BPS is tilted down to reduce ischial support. Specific aim 2: The total and segmental lumbar lordosis, pelvis inclination, and intervertebral spaces of lumbar spine, will be measured using X-ray images and compared under the different sitting conditions. Hypothesis 3: Sitting alternately between the postures with the BPS at level and tilted down positions will reduce the discomfort/pain associated with sitting. As a result, patients with LBP will better tolerate prolonged sitting. Specific aim 3: The subjective evaluation and impressions gained from the use of such a sitting design for a period of four months will be evaluated using questionnaire in two groups of chronic LBP patients with pain history and symptoms.